I finally got my runtime tests with the Pi Zero and Raspberry Pi 3 done, here are the runtime numbers in minutes for all Raspberry Pi's the LiFePO4wered/Pi can work with, tested with both the 3.2V and 5V LiFePO4wered/Pi versions, ordered from best to worst:

All tests were conducted with a freshly charged cell, running the minimal Debian Jessie Lite image, connected to WiFi (using an Edimax USB dongle for all Pi's except the Pi 3, which used its on-board WiFi), an active SSH connection, one run of apt-get update, followed by regular voltage checks using the lifepo4wered-cli tool.

The Pi Zero runs the longest, for just about 2 and a half hours. This is only slightly longer than the Model A+, which makes a very good showing. I will have to experiment with some underclocking and other tricks just to see how long I can make it last, best case.

More surprising is that the Pi 3 seems to be a little more efficient than the Pi 2, which is unexpected considering its higher speed. It probably benefits from the on-board WiFi being more energy efficient than the USB dongle. I can't wait to see what we get when the RPi 3 Model A is released! :)